Optical attenuation coefficients of glacier ice from 350-700 nm and raw irradiance values from 350-900 nm

Optical attenuation coefficients of glacier ice from 350-700 nm were estimated from in-ice solar irradiance measured over the spectral range 350-900 nm and 12-124 cm depth collected at a site in the western Greenland ablation zone (67.15 oN, 50.02 oW). The acquired spectral irradiance measurements are used to calculate irradiance (flux) attenuation coefficients using an exponential decay Bouguer law model. Spectral absorption coefficients are estimated using the method of Warren et. al. (2006), which relates the attenuation coefficient to the absorption coefficient in the visible spectrum. The attenuation coefficients are calculated with linear regression between ice thickness in units of solid ice equivalent referenced to 917 kg/m3 and co-located transmittance. Solid ice equivalent thickness is calculated from in-situ ice density measured in the field on an ice core extracted from the measurement location. The ice density was 699 kg/m3 from 0-8 cm depth, 801 kg/m3 from 4-45 cm , 883 kg/m3 from 45-74 cm, and 888 kg/m3 from 74-122 cm. The depth-weighted ice density in the regions where attenuation was measured was 835 kg/m3 (12-77 cm) and 855 kg/m3 (53-124 cm). The field measurements were completed between 13:45 and 14:35 local time (UTC -3), at solar zenith angles of ~48–51o. Solar noon at this time and location is ~13:26.